The present invention relates to a screening apparatus for grains, seeds or the like materials or granules, comprising a housing wherein a frame structure is arranged which is adapted to be rotated about a main axis and to support screening means eccentrically arranged with respect to the main axis.
An apparatus of the kind referred to above is disclosed in Danish Pat. No. 122,791. The screening means of this known apparatus consist of two screen drums arranged diametrically with respect to the main axis. During the operation of this known screening apparatus, the frame structure and, accordingly, also the screen drums, are driven in a planetary movement about the main axis and simultaneously each of the screen drums performs a rotating movement about its own axis which, accordingly, constitutes a planetary axis. Accordingly, the material which is fed into the screen drums will be subjected to a centrifugal force which partly is due to the rotation of the screen drums themselves, and partly is due to the planetary movement of the screen drums. Such centrifugal force results in that a body of material having a cross section shape generally corresponding to a kidney will adjust itself along the parts of the screen drums which, at any time, face outwardly and such body of material will, provided the peripheral velocities of the drums and the peripheral velocity of the planetary movement are selected appropriately with respect to the material to be screened, move comparatively slowly down through the corresponding drum, and simultaneously the material constituting the body will be tumbled around upon the inner surfaces of the screen means, whereby the desired screening effect is achieved.
Moreover, reference is made to the present inventor's U.S. Pat. No. 4,480,754 in which a screening apparatus is disclosed wherein the eccentricity of the axis of rotation of a screen drum is smaller than the longest radius of the screen drum.